The present invention relates to a method of forming an electron tube which uses a field emission cold cathode device as an electron source, and more particularly to an electric discharge processing method for an electrode in the vicinity of a field emission cold cathode device in an electron tube.
Electron tubes such as Braun tubes and traveling wave tubes are have electron guns. In the past. electron sources for the electron guns have comprised hot cathode such as an oxide cathode to be heated by a heater. In recent years, in place of the hot cathodes as the electron source, a field emission cold cathode has been received a great deal of attention because the field emission cold cathode is advantageous in high current density and a small velocity distribution of emitted electrons as compared to the hot cathode.
If the field emission cold cathode is used as the electron source for the Braun tube, then no power is needed for heating the cathode, resulting in a reduction of a power comsumption. The high current density provided by the field emission cold cathode allows the Brawn tube to have a high resolution. Advantages in characteristics of the field emission cold cathode allows the other electron tubes to exhibit high performances.
FIG. 1 is a fragmentary cross sectional elevation view illustrative of a conventional structure of the field emission cold cathode. An insulation layer 33 is formed over a silicon substrate 34. The insulation layer 33 has a matrix alignment of holes through which surfaces of the silicon substrate 34. Within the holes of the insulation layer 33, a plurality of micro-sized and cone-shaped emitters 32 are aligned over the silicon substrate 34. A gate electrode 31 is formed on a top surface of the insulation layer 33 except over the holes or except over the emitters 32. The gate electrode 31 lies at a near level to tops of the emitters 32. The emitters 32 are applied with a voltage through the silicon substrate 34. The gate electrode 31 is also applied with a different voltage so that a voltage is applied across the gate electrode 31 and the emitters 32, whereby an electric filed is concentrated at the top of each of the emitters 32. The concentration of the electric filed at the top of each of the emitters 32 cause an electron emission from the top of each of the emitters 32.
In Japanese laid-open patent publication No. 9-204880, it is disclosed that in place of the conventional hot cathode, the field emission cold cathode is used as the electron source of the Braun tube.
In Japanese laid-open patent publication No. 10-125242, it is disclosed to use the field emission cold cathode as the electron source of a microwave tube such as the traveling wave tube.
A conventional method of forming the conventional electron tube, for example, the Braun tube using the hot cathode as the electron source will be described. A valve is first formed which accommodates a fluorescent material screen and various internal members before an electron gun mounted with a hot cathode is then placed into a neck of the valve. The value containing the electron gun is further heated for current exhaust to cause a high vacuum in the valve, before the valve is sealed. Furthermore, a getter is flashed to form a getter film on an inside wall of the valve, so that an electric discharge processing process for the electron gun electrode or a high voltage knocking process is carried out in order to have the getter film absorb residual gases in the value to increase the degree of the vacuum. This high voltage knocking process is usually carried out in order to prevent discharge between electrodes of the electron guns in normal operations. FIG. 2 is a diagram illustrative of waveforms of a high voltage pulse applied across a high voltage side electrode and a low voltage side electrode of the electron gun in a high voltage knocking process. A voltage of the pulses is higher by two or three times than the usual voltage in the normal operation. The application of the pulses causes the discharge which eliminate or removes any wound on the electrode surface, and any dusts from the electrode surface.
The conventional field emission cold cathode has a problem with a possible breaking of the device in operation. The emitter and gate electrode are very close to each other so that a discharge is likely to be caused by an influence of a gas whereby a large current flows through the emitter during the discharge process, resulting in that the emitter is broken and a shot circuit is formed between the emitter and the gate electrode.
In order to avoid the above problem, it was proposed that a resistive layer is formed in series to the emitter to suppress or control the current in the discharge process in order to prevent the emitter from being melt and broken. This conventional device still has the following problem. If in the discharge process, a voltage of not more than about several tends voltages is applied across the emitter and the gate electrode, then the resistive layer formed in series to the emitter may prevent the emitter to be melt and broken. If, however, a higher voltage than about several tends voltages is applied across the emitter and the gate electrode, it is possible that the emitter is melt and broken.
As described above, the method of forming the electron tube using the hot cathode utilizes the electric discharge processing or the high voltage knocking process to the electrode, wherein a high voltage pulse is applied across electrodes of the electron gun during manufacturing processes for the Braun tube in order to prevent the discharge between electrodes in operation of the Braun tube. In the high voltage knocking process, discharges are frequency caused at electrodes of the electron guns and the inner walls of the valves in the vicinity of the electron guns. It has also been known to apply the electric discharge processing to other electron tubes than the Braun tube, wherein a high voltage is applied to metal electrodes in the vicinity of the devices.
If the above-described conventional method for forming the electron tube using the hot cathode as the electron source is applied to the electron tube using the field emission cold cathode as the electron source, it is possible that the field emission cold cathode device as the electron source is broken in the electric discharge process. The electron tube structure using the field emission cold cathode device as the electron source has been proposed. No electric discharge processing process to the electrodes in the vicinity of the field emission cold cathode devices in the manufacturing processes has yet been considered and investigated. If no electric discharge processing process is made in the manufacturing processes, it is possible that discharges are caused between the electrodes in operation of the electron tube, whereby the field emission cold cathode devices may be broken to make the electron tube inoperable.
In the above circumstances, it had been required to develop a novel method of electric discharge processing to electrodes in the vicinity of a field emission cold cathode device during manufacturing processes for the electron device which uses the field emission cold cathode device as the electron source free from the above problem.
Accordingly, it is an object of the present invention to provide a novel method of electric discharge processing to electrodes in the vicinity of a field emission cold cathode device during manufacturing processes for the electron device which uses the field emission cold cathode device as the electron source, whereby the electron tube is free from the above problems.
It is a further object of the present invention to provide a novel method of electric discharge processing to electrodes in the vicinity of a field emission cold cathode device during manufacturing processes for the electron device which uses the field emission cold cathode device as the electron source, thereby preventing any discharge between electrodes in the vicinity of the field emission cold cathode device in placing the electron tube in operation.
It is a still further object of the present invention to provide a novel method of electric discharge processing to electrodes in the vicinity of a field emission cold cathode device during manufacturing processes for the electron device which uses the field emission cold cathode device as the electron source, thereby preventing the field emission cold cathode device from being broken in operation.
It is yet a further object of the present invention to provide a novel method of electric discharge processing to electrodes in the vicinity of a field emission cold cathode device during manufacturing processes for the electron device which uses the field emission cold cathode device as the electron source, thereby preventing any excess discharge in the vicinity of the field emission cold cathode device in placing the electron tube in operation.
The present invention provides a method of carrying out an electric discharge processing to an electron tube having a field emission cold cathode device, wherein at least a high voltage electrode of the electron tube is maintained in a high voltage range, whilst all electrodes of the electron tube except for the at least high voltage electrode are maintained in a lower voltage range than the high voltage range.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.